Hunting Horsetails

A few months ago, I got an e-mail from my friend and neighbor Elisabeth. She and I are both members of the New York Fern Society, and e-mails are constantly flying from one member to another about unexpected ferny discoveries. “Dear Oliver,” she wrote:

I noticed a nice clump of big, fat Equisetum hyemale growing on the High Line the other day. It’s on your left as you go uptown, just after crossing over 14th Street. Worth a visit.

Frondly,

Elisabeth

The subject line of the e-mail read “horsetails in the ’hood.”

I have a special, tender feeling for horsetails and other “fern allies” (as they used to be called): club mosses, spike mosses, whisk ferns. In England, before the war, my favorite aunt used to take me on woodland walks, pointing out these plain-looking plants. They lack the showy fronds of ferns. Some of them were pioneers, my aunt told me, the first life on land, hundreds of millions of years ago. In the oxygen-rich atmosphere of the Carboniferous, they had grown gigantic—some were more than a hundred feet tall. What we prosaically called coal, she said, came from the compressed bodies of these giant trees, which had lived and died in the marshes aeons ago. The great horsetail trees, the calamites, had all gone long, long ago, leaving only their miniature descendants. The horsetails she showed me were little more than upright, slender, hollow tubes, growing in clusters about two feet high. I wondered how such a delicate structure could possibly hold itself up, unbuttressed, if it was a hundred feet tall.

I wanted to dash up to the High Line as soon as I got Elisabeth’s e-mail, but obstacles kept arising. Then, blessedly, a free weekend, and a friend to guide me. (I am a bit blind now, and don’t like dealing with crowds or steps without a companion.) So, with my friend Billy, I planned a mini-excursion: we would climb the High Line and hunt for Equisetum hyemale.

The High Line divides into two paths at Fourteenth Street, an upper deck and a lower one perhaps five feet below it. Between them is a median that no one pays much attention to; it is this, the overlooked median, that is covered in horsetails. Horsetails need a lot of water; they like to grow in bogs and marshes or by the sides of rivers. On the High Line they grow next to a little stream running along the median. It was a sultry Saturday, and people had taken off their shoes and socks to dip their feet into the cool water. They seemed to be ignoring the horsetails.

Horsetails have jointed segments telescoping one into the next, the segments getting smaller toward the growing apex. The segments grow smaller in such a regular way that the seventeenth-century Scottish mathematician John Napier, it is said, was inspired by them to invent logarithms. A few of the stems have tiny, tan, whiskery leaves at the joints. The stems themselves are green, and some of them bear little cones at their distal ends, on which the sporangia are clustered. The sporangia are getting tense and ripe, and by midsummer they will dehisce, bursting open to release millions of tiny green spores, their posterity, into the air.

Wanting to get a closer look, I took out my little 4x monocular and, bending slightly, focussed on the horsetails, trying to see the individual sporangia on the cones. My crouching position aroused the attention of a uniformed guard, who thought that I was looking at women’s legs as they waded in the stream on the other side of the horsetail hedge. I assured him that I was only looking at the horsetails, and he smiled, taking the word as slang for some part of the female anatomy. He moved on, smirking, assuming that I was just another harmless, elderly voyeur. He was right, in a way—I was looking for sporangia, spying on the sex life of horsetails.

Billy asked why I like the horsetails so much. I think it is a combination of their simplicity, their antiquity, and their mathematical elegance. I like the way they are filled with silica—their popular name is “scouring rush,” and I have a bottle of Heavenly Horsetail All-Purpose Cleaner by the sink. Silicon is not too common an element in living creatures. I like their shape, their jointedness, like tiny bamboos. Of course, horsetails are nothing like bamboo in other ways. Bamboos are flowering grasses, only sixty million years old, whereas horsetails and their relatives go back to a time long before flowering plants arose.

All too soon, the High Line’s island of horsetails came to an end, and, after a dream of deep time, I was back in the noisy bustle of the twenty-first century. ♦

Oliver Sacks, a professor of neurology at the N.Y.U. School of Medicine, is the author of “Awakenings,” “Musicophilia,” and many other books. His memoir, “On the Move,” was published in April.